Singer Pete Doherty is in custody at a north London police station after being arrested on suspicion of theft and assault on Wednesday evening.
Doherty left The Libertines following high-profile drug problems
The former Libertines frontman was held after an alleged incident at a hotel in Clerkenwell, central London.
Film-maker Max Carlish told the BBC he had been attacked by Doherty, but would not be pressing charges against him.
Carlish said he had sold photographs showing Doherty taking heroin to a Sunday newspaper.
Carlish, who had been making a documentary about Doherty's band Babyshambles, told Radio 1 Entertainment News: "I'm feeling bloody battered, but I'm bowed and I feel sorry for Pete. My heart goes out to Pete, he has screwed up big time now.
"Frankly, I wouldn't be surprised if in three weeks time he's hanging on the end of a rope in a jail cell somewhere. I do not want that to happen, so I'm not going to press charges.
"Pete may be thinking 'I can't stand Max now', but I still love Pete and I want the best for him.
"If that involves me giving him money so he can go into rehabilitation, the money I've earned from the Mirror and the people who are waving cheques in my face, then so be it."
A police spokesperson told reporters outside Islington police station: "We were called at approximately 6.20pm on Wednesday to a hotel on Peter's Lane, EC1, to reports of a man having been assaulted.
"A 25-year-old man was arrested on suspicion of actual bodily harm and theft.
"He was taken to a north London police station where he was re-arrested on suspicion of actual bodily harm and robbery."
Doherty, 25, parted company with The Libertines after failing to curb his drug problems but continued to perform as part of Babyshambles.
The self-confessed crack cocaine addict claimed to have spent £1,000 a day in the past on his drug habit.
Doherty (right) was jailed in 2003 for a burglary at Barat's home (left)
He was jailed for six months for burgling the house of Libertines bandmate Carl Barat in 2003.
Last September he received a four-month suspended jail sentence for possession of a flick knife.
Interest in Doherty has recently expanded beyond fans of his music after he began a relationship with model Kate Moss.
Babyshambles, who scored a UK top 10 hit with the single Killamangiro, will compete with The Libertines for the title of best live band at the NME Awards on 17 February.